1. Field of the Invention
This invention relates to apparatus for automatically assemblying electronic components on printed circuit boards and has particular reference to a feeding device for feeding such components to a pickup station from which the components are transported by a "pick and place" device to a specific location on the surface of a printed circuit board.
2. Description of The Prior Art
Component placement apparatus are well known in which electronic components, such as diodes, resistors, capacitors and the like are surface mounted in desired locations on a printed circuit board preparatory to bonding the same to selected circuit conductors on the board. The components are generally of miniature size and are mounted along a transport tape which is incrementally advanced to feed the components, one at a time, to the pickup station. The transport tape generally comprises a flexible carrier strip having receptacles formed therealong to contain the components and a retainer or cover strip adhesively secured to the carrier strip. Just prior to reaching the pickup station the cover strip is stripped from the carrier tape to permit removal of the uncovered component by the "pick and place unit".
Generally, a relatively large number of feeding devices carrying respective component transport tapes are mounted on one or more carriages which are stepped along a path to sequentially position different ones of the feeding devices at the pickup station. Since the components must be precisely located at the pickup station, a high degree of accuracy must be maintained in positioning the feeding devices and in advancing the transport tapes.
One of the problems encountered in feeding such transport tapes is that since the tapes usually are made of relatively flexible and very thin material, such as plastic, they tend to stretch or distort when operated at high intermittent speeds and thus become inaccurate in placement of the components at the pickup station. This is accentuated by variation in tension in the tapes resulting from stripping the cover strip from the carrier strip.
Although prior feeding devices have been generally satisfactory, they are relatively complicated and expensive to manufacture and tend to become unreliable at higher speeds. Also, since a large number of feeding devices are usually required to provide different sizes and types of components for a typical circuit board, the cost of such component feeding devices is of paramount importance.